Display fields of a given plist file, if second parameter filter (like regexp) by it

plistread.rb

#!/usr/bin/env ruby
# plistread.rb

require 'plist'

if ARGV.length == 0
    puts "Use: plistread.rb file.plist [attribute]"
    exit 0
end

filter = case ARGV.length
    when 1 then /.*/
    when 2 then /#{ARGV[1]}/
    end

Plist::parse_xml(ARGV[0]).sort.each {|k, v|
    puts("%40s: %s" % [k, v.to_s]) if k =~ filter
}